The lateral cochlear wall maintains the ionic metabolism necessary for normal cochlear physiology, and disruption of lateral cochlear wall function - by genetic or environmental insults - leads to hearing loss. Despite the importance of this structure, little is known about its normal growth and development, and there are currently no means to repair this structure once it is damaged. Here, we propose to develop genetic and stem cell-based approaches necessary to accelerate research in a component of the lateral wall, the spiral ligament, whose integrity is vital for lateral wall function. The ultimate goal of this proposal is to develop stem cell-based therapies to correct hearing loss in an animal model of spiral ligament dysfunction, the Brn4/Pou3f3 mutant. To effectively implement and optimize the use of stem cells, a fundamental understanding of the basic biology of growth and differentiation of the spiral ligaments is necessary. In particular, knowledge of the cell signaling pathways that support the growth and maintenance of spiral ligament fibrocytes will be key to optimizing stem cell approaches. Therefore, early in the grant-funding period, we propose to characterize the growth factors that normally regulate spiral ligament fibrocytes. Subsequently, once we have developed a working model of stem cell therapy in mice, we can use our knowledge of fibrocyte growth factor regulation to design rational approaches to optimize the targeting and growth of stem cells in the spiral ligament. Additionally, we propose to develop a powerful, versatile genetic tool to express genes, including the relevant growth factors, in the spiral ligament. Using a previously characterized otic enhancer from the Brn4 gene, we will express the Tet- On version of the tetracycline-inducible gene expression system in cochlear fibrocytes. Each of these tools/approaches alone has great potential to enhance our understanding of the development, physiology and function of the spiral ligament. However, in conjunction, these tools/approaches will synergize to accelerate experimentation on the lateral cochlear wall, and optimize our ability to replenish spiral fibrocytes in animal models of hearing loss using stem cell therapy. PUBLIC HEALTH RELEVANCE: Stem cell therapies hold tremendous promise for reconstructing or replacing tissue damaged by genetic or environmental insults. Here, we propose to develop stem cell approaches to reverse damage of the spiral ligament, a structure that is necessary to maintain the proper ionic environment in the inner ear. By developing powerful experimental tools, we will accelerate research that can help to cure or ameliorate hearing loss.